Congestive heart failure (CHF) is a condition where the heart is not able to pump enough blood to supply the body with energy and oxygen. There are multiple causes for the heart to fail, such as ischemic heart disease caused by clogged arteries, cardiomyopathy of unknown reasons or end stage after congenital heart diseases or heart valve diseases. With an increasing aging of the population today, the problem of CHF is increasing and is now the most common cause of heart disease mortality. According to the American Heart Association 5 million people in the United States experience CHF, increasing in number by half a million every year. 1% of the population over 50 years of age or 5% of the more than 75 years old are affected by the condition of CHF. Worldwide the number of people suffering from CHD is estimated around 20 million. Independent of what the reason for CHD, the symptoms and the treatment are the same. The failing pump function causes low blood pressure and low cardiac output resulting in renal failure, and a lower urine production causes fluid retention in the body.
A failing left ventricle of the heart causes the blood to be stagnant in the lungs, causing slow flow and high pressures in the blood stream of the lungs. As a result thereof, fluid will be pressed from the blood vessels into the lung tissue resulting in a decreased gas exchange in the lungs, a condition that worsens the heart condition.
A right heart failure on the other hand causes slow flow and stagnation of blood in the vein system of the body. As a result thereof, fluid is pressed from the small blood vessels, the capillaries, into the various organ tissues including the fatty tissue under the skin. This fluid retention causes for instance weight gain, swollen organs and legs and shortness of breath.
The treatment of CHF is first of all a correction of the underlying causes such as valvular disease or coronary artery blocks. However, for the majority of patients this treatment is too late. Surgically, only heart transplantation and implantation of mechanical heart assist devices are available. However, only 2-3000 heart transplants are made worldwide in the youngest population, due to lack of donor organs. Also, mechanical assist devices are still experimental. Therefore the majority of the patients are left with symptomatic medical treatment. First of all fluid restriction and treatment with diuretics are used. Other drugs are Angiotensin-converting Enzyme (ACE) inhibitors, beta-blockers and digitalis. Most of CHF patients live for a long time before dying and are readmitted again and again in order to adjust medication or get diuretics injected. Changes in the heart movements, the volumes and the pressures occur fast. The symptoms, however, appear slowly, resulting in treatment too late.
Previously, Medtronic Inc. has introduced the Chronicle device, an implantable Hemodynamic Monitor. That system contains a Lithium battery and a computing element to be implanted under the skin, remote from the heart. Further, this unit has a lead with a pressure transducer that extends into the heart where it can measure intra cardiac pressure, an indirect indicator when diagnosing a heart condition. The Chronicle unit is capable of using several algorithms to present curves and trends that can be detected in a receiver outside the body.
Savacor Inc. has developed the HeartPOD™, a very similar product to the Chronicle device, the major difference being that the transducer located at the tip of a lead is implanted in the atrial septum wall measuring the pressure in the left atrium. A handheld computer serves as a patient monitor receiving physiological signals from an implant by wireless transmission. Savacor's technology is based on apparatus and methods as described in U.S. Pat. No. 6,328,699.
U.S. Pat. No. 6,328,699 discloses an apparatus for treating congestive heart failure in a patient. However, this apparatus is provided with a pressure transducer lead that is permanently implanted in the left atrium of the patients heart. This pressure transducer lead is connected to an electrical circuitry for processing electrical signals. Thus, the apparatus according to U.S. Pat. No. 6,328,699 has the disadvantage of presenting a lead (or wire) inside the body (and inside the heart) of the patient, rendering the apparatus inferior in respect of a device in no need of such a lead, said device being fully implantable in the body of the patient. Moreover, the device according to U.S. Pat. No. 6,328,699 receives energy from a battery, which renders it inferior inn comparison to a device in no need of a battery.
Remon Medical Technologies Inc. has introduced a device for non-invasive assessment of pulmonary artery pressure. A pressure transducer is inserted into the pulmonary artery and fixed there. The pressure transducer is connected to an implanted remote device collecting data from the implanted transducer. Ultrasound energy is applied from outside the body in order to activate and energize the device. Wireless communication to an external unit is also supported when the device is powered-up.
CardioMEMS Inc. on the other hand has developed a similar system that can measure pressure by means of an un-powered, permanently implantable pressure sensor, which is energized by means of high frequency radio waves from outside the body. The pressure sensor is intended for measuring intrasac pressure during endovascular abdominal aortic aneurysm (AAA) repair.
Disturbances of the Heart Rhythm
Pacemakers (PM) are electronic devices to be implanted in a human body with the purpose to regulate the heart beat and the heart rhythm by means of electrical stimuli in patients that have lost the ability to regulate the heart rhythm, e.g. a heart block is such a condition. A PM 36, e.g. shown in FIG. 2, is a hermetically sealed metal can 38 that contains a battery 40 and an electronic circuit. The PM can is implanted in the body under the skin at a remote site from the heart. The PM delivers electrical stimuli to the heart by means of an electrical lead 42, or multiple electrical leads 42, extending from the PM can 38 in one end to a heart tissue and in the other end having an un-insulated electrode tip 44 or another form of transducer at tip 44, respectively.
Rune Elmqvist, a Swedish engineer designed the first implantable PM, and Dr. Aake Senning implanted the device into the body of the patient Arne Larsson in 1958. The patient lived for 43 years after the first implant and had additionally 23 different PMs implanted during his lifetime. This first PM had a battery that was rechargeable, the first non rechargeable PM was developed simultaneously by Dr. Greatbach in USA and was implanted for the first time in 1960. Today only non-rechargeable PMs are used. The PM industry today is among the most profitable in the medical device area, more than 600,000 PMs are produced yearly. Some modern PMs are able also to detect irregular, sometimes life-threatening irregularities in the heart rhythm, also known as arrhythmia. Over time, PMs were combined with a defibrillator, called an implantable cardioverter defibrillator (ICD), to correct such arrhythmia by means of an electrical shock.
Generally, there are two main problems with PM treatment today, related to the leads and to the battery.
The leads are insulated cables, connected hermetically sealed to the electronic circuit in the PM can in one end and connected to the heart tissue with an un-insulated end, the electrode tip, in the other end. The tip is made of material that facilitates in-growth in the heart tissue. The insulation is made of medical quality polymers, usually polyurethane and is made as thin as possible in order to save space. The insulation must be absolutely impermeable. If not, electrical leak currents will occur and the PM will not function. The core of the lead, the electrically conducting part, is made of a metal that is a good electrical conductor. Since the heart is constantly bending and twisting, the metal in the conductor has to be very tolerant to bending without fracturing, a fracture occurs frequently and stops the electron transfer and the PM does not function. Lead infection is another large problem. Furthermore, the leads are immersed in the blood stream, a perfect environment for bacteria, and in contact with subcutaneous tissue, a common site for infections, especially from the PM can pocket. Bacteria easily migrate from the skin to subcutaneous tissue and into the blood stream along the leads. Finally lead tips often dislocate from the heart tissue, loosing contact to the heart cells, and thereby no electron transfer to the heart tissue is possible. Insulation defects, conductor fracture, infections, and tip dislocations are some of the PM related issues that result in recurrent surgical operations, usually including additional leads being put in, since retrieval of previously implanted leads is very difficult if not impossible in many cases. Thus patients normally end up having many leads, most of them not in use. When more complex devices are used, like an ICD or a PM that stimulates and detects at different sites in the heart (e.g. atrium and ventricle) a system may consist of up to four leads at implant, each of them prone to the problems described above.
The Battery
Different energy sources have been explored for batteries, inclusive nuclear. However, only Lithium (Li) batteries have proven to function well in PMs and today this energy source is exclusively used. Like all batteries the main problem is durability. The electrons will only flow through a closed circuit, from the negative pole of a battery through the load, i.e. the body, back to the positive pole of a battery, and then through the battery (electrical current is described in the opposite direction). Electrons returning to the battery join with Iodine and then with Lithium to Lithium-Iodine (LiI), which is not a good electron conductor. Buildup of LiI increases the internal resistance in a Li battery. Increasing internal resistance causes a decreasing battery voltage and finally the available voltage becomes insufficient to stimulate the heart and the battery is useless. A Li battery will deliver at its beginning-of-life around 2.8 V and in the best case it will have a linear output for 5 years. From this time the internal resistance increases exponentially, and when the voltage comes down to close to the heart stimulation threshold, the battery has to be replaced. A Li battery will normally contain 2 Ah (ampere-hours) of capacity, the drain is typically 25 microamperes, giving a battery a theoretical lifetime of 80 000 hours. In reality, however, they seldom last longer than 5 years.
As one may see, the main problems related to PM treatment are related to the battery and to the leads.
Several attempts have been made to solve these problems.
For instance, W. H. Ko, in U.S. Pat. No. 3,456,134, as published Jul. 15, 1969, discloses a piezoelectric converter for converting body motion to electrical energy for driving electrical implants, such as a PM. Ko found that this piezoelectric system may deliver enough energy to run a PM when driven at a mechanical pulse rate and with a motion similar to the heart motion of an animal, upon which it was tested. However he did neither suggested to integrate a piezoelectric system in a PM itself nor to implant such a conversion device in a heart. As nearly 40 years have passed since the disclosure of Ko, and no commercially available PMs using Kos principle have become available, it is regarded that the skilled person in the field of implanted devices does not regard that it is feasible to carry out Kos piezoelectric system with implantable devices.
U.S. Pat. No. 6,654,638 discloses ultrasonically activated electrodes that generally use a piezoelectric energy converter to convert energy from an external energy source, e.g. an ultrasonic element. This energy is stored within the electrode. It is also mentioned that the electrodes may use the contracting heart to produce energy by compressing or deflecting a piezoelectric element. However, the electrodes disclosed in U.S. Pat. No. 6,654,638 are always controlled by an external device. That means pacing action is not possible by the electrode itself without the interaction with an external control unit. Furthermore, also the piezoelectric element is integrated into the housing of the electrode, whereby the piezoelectric element uses valuable space of the housing's surface that no longer is available for use as an electrode surface.
Hence, there is a need for a device which alleviates or avoids problems such as, but not limited to, those mentioned above, and which device is fully implantable in the body, such as in the vicinity of, or inside, the heart, of a patient, which device may be used for instance for CHF cases, but also in acute situations in the intensive care unit for patients suffering from acute heart failure, for instance after large myocardial infarctions, after catheter based coronary artery operation or after cardiac surgery, which device is in no need of battery (or batteries) or lead(s), which device may continuously monitor the heart function and may initiate early medical counter measures.